Have you ever taken a bite of lettuce and thought, “Boy this lettuce was really sweet last week but now it is a little bitter?” It happens. Many factors can cause lettuce to become bitter, but the most frequent is the age of the lettuce plant and the amount of heat to which it is exposed.
There are a few other factors too and most of them can be remedied easily. It is not possible to remedy age and temperature, but you can try to fool the lettuce into thinking it is still young and that the temperature is not that hot.
Heat and Age
Lettuce is a cold weather crop, which is why it is planted in the early spring or late fall. When it starts to get hot in mid-July, lettuce tends to bolt.
This means it sends out a stalk and flowers and this is normal maturation process of the plant. Any lettuce that is produced while this is happening will be bitter.
Lettuce is good from 45 to 65 degrees F and once it starts to move into the 75 degree range, it starts to bolt and become bitter. Fool the lettuce into thinking it is cooler than it is by mulching the roots.
A 3 to 4 inch layer of mulch keeps the roots cool and the lettuce does not realize the heat is increasing.
Another way to fool the lettuce is to plant some of it in partial shade. Plant it under a tree or between tomatoes or let it be shaded by cucumbers growing up a trellis.
This will give the lettuce plants more time to grow before they realize the weather is getting hot.
Too Little Water
It actually should never get to the point where the edges start turning brown.
Lettuce needs supplemental water frequently so that the leaves continue to stay moist and full. When you do water, don’t just stand there with a hose in your hand.
Put a sprinkler on or use ground irrigation hoses that drip water directly to the roots of the plant. Water so you get at least 1 inch of water into the roots of the plants. I put out an empty tin can that fills with water from my sprinkler.
I measure to make sure 1 inch has been caught in the can. During dry periods, I may even water 2 inches at a time. Never let the lettuce bed become dry. It needs to be evenly moist at all times.
Lettuce needs nutrients to grow or it will never mature and the flavor is horribly bitter. Before even planting lettuce make sure to amend the soil, every year, with at least 4 inches of compost dug into the ground where you will plant.
You might also want to think about fertilizing at least 1 time when you plant in the spring and a second time when you plant in the fall.
Use a high nitrogen fertilizer since that encourages growth of green leaves. However, if you fertilize too much, the lettuce can still turn bitter.
Don’t overdo it. If your fertilized lettuce starts to take on a bitter flavor, treat the soil with some wood ash, digging it in around the roots of the lettuce. That should sweeten it up.
Aster Yellows is a disease that some types of lettuce can get and it causes bitterness. Outer leaves of lettuce become small and stunted and everything starts to twist and become deformed.
The leaves also lose their color and become yellowed. Just discard the plant safely and avoid planting in the area for a season.
Even if your lettuce is a little old and the temperature is hot, you can still salvage the lettuce at the end of the growing period. Take a big pale of cold water with you into the garden when you harvest your lettuce.
Bring it in the house and put into a bowl of clean cold water and soak 1 hour. Dry off the lettuce and put it in a plastic bag in the refrigerator 24 to 48 hours before using and the bitterness will disappear.
Look for lettuce varieties that tolerate warm weather better as there are some that do. Plant different varieties of leaf and head lettuce and plant one batch one week, wait a week and plant another so you have a continuous supply of sweet lettuce until mid-summer.
Start planting again when the temperature starts to cool in the fall for a second harvest. Treat old lettuce with the cold water method to extend the amount you get out of your garden and turn bitter lettuce back into tasty lettuce.